Death metal, and in fact, most of modern metal originated from underground bands during the hair metal days, and most of the bigger ones hail from Sweden, particularly Gothenburg. The exceptions to this are nu-metal, which is based in more than one way off of grunge, and classic/stoner rock. The music generally consists of screams and yells, more high-pitched than not. They also have utter walls of guitar, accompanied by difficult-to-play leads, and drumwork second only to jazz. Also tends to have a recurring bass line; and guitars are oftened tuned down two steps or more. They sometimes tend to have a softer side as well, with orchestras or pianists. Lyrics, however hard to hear, are normally about important issues relating to the state of things, personal conflict, or political anthems. Major names from this genre: Arch Enemy, Opeth (much more of a softer side than most, one of the best bands there is), Soilwork, In Flames, Dark Tranquil(l)ity, etc. On another note, people who listen to nothing but metal tend to be fiercely defensive of their favorite bands, and do not like change, as any In Flames fan will tell you. They tend to have a love/hate relationship with any band they listen to. I personally don't think there is such thing as a bad song, just a less good one.

Death metal is a relitively younge gendre of music, but it has been plaqued by controversy throughout it's entire life. Death metal is characterised by it's gutteral vocal assault, jinsane double bass drumming and heavily distorted and detuned guitars. Death metal can be painfully stupid and cliché (Cannibal Corpse, Deicide) to stunningly complex and rousing (Meshuggah, Opeth, Satrycon. Ultimatly it's all music and deserves it's repect. People often associate death metal with poor musicainship and juvinile lyric themes, although some bands adhere to this formula it's not always the case as with any gendre of music. Death metal takes loads of talent to perform, and most of it shoots right over the casual listener's head. The lyrical themes in death metal can seem one-dimenional but reads some lyrics and you'll be astonished (try Napalm Death) How the gendre got it's name can be daebated but I think it got it's name from the Venom album (Black Metal)

Death metal is a subgenre of heavy metal generally involving low tuned guitars played with tremolo picking and many solos, double kick or blast beat drumming techniques, minor keys or atonality, and rapid time signature changes, chromatic chord progressions, and intricate song-writing. Death metal is the most underrated and underappreciated genre in music, with many of the most famous bands full of world class musicians that taught at the most prestigious music schools in the world. The best aspects of every genre of music (new wave of British heavy metal, classical musical, thrash metal, grindcore, black metal and jazz) can be found in death metal albums articulated in a more intelligent and enjoyable manner than in the aforementioned genres. Examples are Atheist's take on jazz, Arghoslent's NWOBHM riffs, Necrophagist's Beethoven-influenced riffs, and Appalling Spawn's grindcore elements. Death metal produces the most thought-provoking and intelligent lyrics of any genre as referenced below.

Guy 1: Why do you think death metal appeals almost exclusively to very intelligent people?
Guy 2: As illuminated in the documentary The Boy With the Incredible Brain, many very high IQ people think in terms of shapes and music that forms shapes. It is not hard to understand why the ebb and flow of death metal riffs appeal almost exclusively to very intelligent people who sense and recognize the shape and contours of the very intricate and highly educated music that is death metal.

Guy 1: What are some death metal songs which shed light not only on natural aspects of the human condition, but more generally on important societal problems directly connected to people's thinking?
Guy 2: Enthralled in Essence (Atheist), Slaughter of Innocence, Demise of the Clone (Suffocation), Mirrors of Reason (Monstrosity), Omnipresent Perception (Beyond Creation), Dethrone the Hypocrites (Anata), Closeminded Failure (Solstice), The Truth About Lies (Krabathor), Lack of Comprehension (Death), Scavenger of Human Sorrow (Death), The Sadistic Motives Behind Bereavement Letters (Arsis) and Shallow Disbelief (Experiment Fear) all have very intelligent messages meeting your requirements.